Friday, May 8, 2009

Nutsedge is Back Again

From Dr. Joe Neal:

Yellow and purple nutsedge are up and growing vigorously. Hand weeding nutsedge is possible early in the season before rhizomes have formed. But, plants have already started producing rhizomes and “daughter” plants. Once this occurs, hand weeding usually results in breaking the stem below ground and a new plant emerging in a day or two.

Spot spraying with a systemic herbicide such as glyphosate will control emerged nutsedge, but the sprouts below ground generally keep emerging. Many landscapers prefer halosulfuron (Sedgehammer) because it controls emerged nutsedge as well as leaving a residual that prevents new nutsedge from emerging for about 4 weeks. Sedgehammer works slowly but can be tank mixed with faster acting postemergence herbicides to achieve rapid kill and residual control. Combinations with glufosinate, glyphosate, or bentazon have been effective for this purpose.

If you have nutsedge in your beds, it is also a good idea to consider preemergence treatments. Pennant Magnum, Freehand, and Tower each will suppress yellow nutsedge. Note I said suppress not “control”. Perhaps a more accurate term would be “partial control”. So even if you have used one of these preemergence herbicides, you will need to be prepared to return to the bed with a postemergence control program -- that will likely even require some hand weeding.

For more information on yellow and purple nutsedge identification and control, follow this link to Horticulture Information Leaflet number 647 -- Nutsedge

For more information contact your local Cooperative Extension Center and ask for the Commercial Horticulture Agent.